The aim of the proposed research is to determine the order and function of the genes in a parainfluenza viral genome in order to better understand the replication of this group of viruses whose single-stranded genome is complementary to mRNA. We propose to: (a) map the position of the viral mRNAs on the viral minus strand genome: this will be done by annealing studies using specific fragments of the viral genome and also by direct visualization of the mRNA-viral genome complex in the electron microscope (b) translate each mRNA in vitro and identify which of the structural polypeptides they code for, and (c) map the position of ts mutations through the construction of heteroduplex ds-RNAs.